CSS: An Overview Forum

What are ems?

Okay so, I am not really sure of what the em unit is. The lesson states: "The font-size unit em is a relative measure: one em is equal to the default font size on whatever screen the user is using."
What is meant by the default font size of the screen?

Em's are just something written into each computer/phone. When it sees an em, it sees a certain size in which to put text. This is because, if I wrote a program on my massive screen, and then you tried to use it on your tiny iphone, it may be too big for your iphone screen, so em's "standardize" in a sense. It is like me saying to you that my desk is two arms wide. Your measurement would be different because you may have longer arms than mine. I hope that helps.